HYDROZOIDS AND CORALS. 119 



the base or poiat of attachment. Cells distinctly lined within, 

 and covered externally by rather thick, wrinkled epitheca. 



Horizon and localities. — Lower Carboniferons, Kinder- 

 hook limestone : Clarksville and Louisiana ( Pike county ). 



Generically Oonopterinmis clearly distinct from Palseacis 

 and Sphenopterium. The corallites are much smaller and* 

 more variable in size than in any known species of the two . 

 genera mentioned. The coralla appear to have been attached 

 to molluscan shells or other submerged objects; and as they 

 grew to be of large size, the lower or marginal cells adhered 

 firmly to the surface of attachment. 



CleistoDora olacenta (WhiteJ. 



Platexiv, fig. 11. 

 MichUinia placenta White, 1883 : Twelfth Ann. Kep. U. S. Geol. and Geog. 

 Sur., p. 157, pi. xxxix, figs. 2a-b. 



Very similar to L. typa, but much larger ; the corallites 

 have a diameter two to three times the size of the typical spe- 

 cies, while the coralla attain a measurement of 10 to 14 cm. 



Horizon and localities. — Lower Carboniferous, Chouteau 

 limestone : Sedalia, Curryville (Pike county). 



The species under consideration is seldom well preserved, 

 and its structural characters are consequently usually difficult 

 to make out satisfactorily. It appears beyond doubt that this 

 form is not properly a Michilinia ; and there are good reasons 

 for believing that it is congeneric with Winchell's Leptopora 

 typa^ though the exact systematic position of that genus has 

 not as yet been made out fully. 



From a comparison of a large series of specimens from 

 White's original locality it would seem that the two species 

 that he recognized are indentical. 



Cleistopora typa Winchell. 



Leptopora typa Winchell, 1863: Proc. Acad. Nat. Sci., Phila., p. 3. 

 Leptopora typa White, 1883 : Ge.l. and Geog. Sur. Ter. , 12th Ann. Rep., 



p. 122, pi. xxxiv, figs. 12a-b. 

 Leptopora gorbyi Miller, 1891: Geol. Sur. Indiana, 17th Ann. Rep., Ad. 

 Sheets, p. 6, pi. 1, figs. 1-4. 



Corallum forming thin discoidal expansions ; with a well- 

 defined, concentrically wrinkled epitheca. Corallities few, 



